A vertical cavity surface emitting laser (VCSEL) is a semiconductor laser diode that can be fabricated using well-known wafer processing techniques. Conventionally, such techniques fabricate a larger number of VCSELs on a single wafer. The wafer is then sawn, scribed, or otherwise divided into a dice, with each die containing at least one VCSEL and possibly other integrated circuitry that was formed on the wafer. The dice are then packaged for use.
A common use of a VCSEL is in generation of an optical signal for transmission on an optical fiber. In this application, the optical signal from the VCSEL generally enters the optical fiber via an optical coupler or port. For efficient coupling of the optical energy from the VCSEL into the optical fiber, the VCSEL and the optical fiber must be aligned so that the beam intensity profile of the VCSEL lies primarily on the core of the optical fiber. An optical system between the VCSEL and the optical fiber can be used to improve the coupling efficiency and increase alignment tolerance of the VCSEL and the optical fiber. In particular, a common optical system for such use includes one or multiple optical elements that focuses and/or manipulate the profile of the light beam on the end of the optical fiber. In the following discussion, lens refers to any optical element that can manipulate the profile of a light beam and can be a refractive or diffractive element.
Forming a lens directly on the emitting area of the VCSEL generally fails to achieve adequate optical performance because it is difficult to make a lens with a short enough focal length to properly focus or collimate the beam. Accordingly, air gaps or separations between the lens and light emitting area of the VCSEL are normally required for processing the optical signal. Further, lens material on an active region of the VCSEL can compromise the reliability of the VCSEL by introducing interface stress. The lens material on the front facet of a VCSEL may also change the reflectivity of the front mirror of the VCSEL, requiring a redesign of the VCSEL.
Making the lenses part of the package or assembly containing the VCSEL allows use of a longer focal length lens element with an air gap. However, a drawback of optical packages or assemblies employing a lens between the VCSEL and the fiber is the need to align the VCSEL, the lens, and the optical fiber. Aligning a lens to a VCSEL on a die generally requires precision instruments and can be a time consuming and therefore expensive process. Structures and methods that reduce the cost associated with combining a VCSEL with a lens are thus sought.